Various disclosures exist in the art in regard to hybrid silica binders which contain one component derived from colloidal silica and another component derived from an organic silicate (e.g., tetraethyl silicate). U.S. Pat. Nos. 2,842,445 and 3,576,652 have been characterized as showing binder formulations prepared with low colloidal silica sol and high organic ethyl silicate volumes. U.S. Pat. No. 3,682,668 to Fujita et al. has been characterized as showing high organic ethyl silicate levels. All three of these patents are indicated as being "binders of alcoholic base" (see U.S. Pat. No. 3,961,968 at Col. 1, lines 46-63, for example).
U.S. Pat. No. 3,961,968 to W. F. Wales describes hybrid binders for ceramic molds where the silica ratio (i.e., SiO.sub.2 content ratio) between organic and inorganic constituents is controlled in the range of 0.09 to 0.9 with a teaching of preferred levels of organic silicate of only 5-10 vol % with the colloidal silica sol range being in the range of 30-75 vol %. This patent advocates use of a glycol ether solvent in excess (i.e., 66.6% or greater based on the total amount of glycol ether and alcohol) to any amounts of alcohol that might be present.
U.S. Pat. No. 4,378,996 to D. Yarwood also generally relates to hybrid binders of organic silicates and inorganic sols in which the resulting "stable" product preferably has a greater than 50% SiO.sub.2 (silica) derivation attributable to the silica sol made possible by a reduction in the amount of water in the silica sol component by either dewatering the sol (e.g., by distillation under reduced pressure) or by replacing the water with a polyhydric alcohol, such as ethylene glycol. Although this patent speaks of replacing the water in the sol with a polyhydric alcohol, it does not indicate that light organic fractions (such as alcohol by-product from the hydrolysis of the organic silicate) are to be removed from the hybrid binder.